JP6271899B2 - Image heating apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image heating apparatus of a divided heater system such as a thermal head in which a large number of heating elements are arranged in the paper width direction, and an image forming apparatus equipped with the same.

  Examples of the image heating device include a fixing device that fixes an unfixed toner image formed on a recording material (recording medium: hereinafter referred to as paper) as a fixed image. Further, a glossiness adjusting device (image modifying device) that adjusts the surface gloss of the image by reheating the toner image that has been semi-fixed or fixed on the paper can be used.

  The image forming apparatus forms a toner image on a sheet using an image forming process such as an electrophotographic image forming system, an electrostatic recording image forming system, a magnetic recording image forming system, or the like. For example, a copying machine, a printer (laser beam printer, LED printer, etc.), a facsimile machine, a multi-function machine thereof, a word processor, and the like are included.

  Paper (recording material) is a sheet-like member on which a toner image is formed by an image forming apparatus. For example, regular or irregular plain paper, cardboard, envelope, postcard, seal, resin sheet, OHT sheet, glossy paper Etc. are included.

  As an image heating apparatus, unlike a ceramic heater or a halogen heater system, there is a split heater system apparatus such as a thermal head in which a large number of heating elements are arranged in the paper width direction. Patent Document 1 is an example of using a thermal head for toner fixing. This is to turn on the heating element at the location where the toner is present (sheet passing portion) and to turn off the heating element where there is no toner (non-sheet passing portion) corresponding to the print data. In the case of the divided heater system, it is not necessary to supply power to the heating element facing the non-sheet passing portion in the case of a small size job with a narrow paper width. This is also a feature of using a divided heater.

JP-A-8-152807

However, when a large-size job is executed following a small-size job, the temperature of the non-sheet passing area at the time of the small size is too low compared to the center. Therefore, after completing a small job and before executing a large job, it is necessary to normalize the temperature distribution by heating here to suppress the occurrence of image defects, conveyance defects, and paper wrinkles due to the above situation. You will be forced to have sex and take time to do so.
Also,

The present invention has been proposed in view of the above problems. The purpose is to reduce image quality , conveyance failure, paper without causing a decrease in productivity due to downtime, etc., even when the width is changed from a small size recording material to a large size recording material. An object of the present invention is to allow the image heating process without wrinkles to be continued.

In order to achieve the above object, a typical configuration of an image heating apparatus according to the present invention includes a heating rotator and a nip portion that sandwiches and conveys a recording material carrying an image between the heating rotator and heats the recording material. And a heating body that heats the heating rotator, arranged side by side along the longitudinal direction of the heating rotator, and individually heated to generate heat. When the apparatus is started up, energization of all of the plurality of heating elements is started and a recording material having a width smaller than the maximum width recording material that can be introduced into the apparatus is continuously introduced. Then, when heating, the temperature of the portion corresponding to the recording material passage portion of the heating rotator is put into the heating element corresponding to the recording material passage portion so that the temperature is maintained at a predetermined image fixing temperature. The amount of power to be controlled is controlled and the recording material of the pressure rotator is not passed. In the recording material non-passing portion so that the difference between the temperature of the portion corresponding to the recording portion and the temperature of the portion corresponding to the recording material passing portion of the pressure rotating body is maintained in a range of ± 20 ° C. Controls the amount of power input to the corresponding heating element, stops supplying power to all the heating elements when the introduction of the set number of recording materials and the heat treatment are completed, and keeps the device in a standby state And a control unit.

In the present invention, during a small-size job for a small-size recording material, a recording material non-passing portion that originally does not need to be heated is also predeterminedly heated. As a result, even when the paper width is changed from a small-size recording material to a large-size recording material, image heating that does not cause image defects , conveyance defects, and paper wrinkles without causing a decrease in productivity due to downtime or the like. Processing can be continued.

FIG. 4 is an enlarged cross-sectional right side schematic view of a main part of a fixing device in a reference example and a block diagram of a control system. FIG. 4A is a schematic front view of an intermediate part omitted in the main part of the fixing device, and FIG. 4B is a schematic diagram illustrating a layer structure of a belt. 2 is a schematic configuration diagram of an image forming apparatus in a reference example . (A) is a schematic enlarged cross-sectional view of the heater, and (b) is a schematic diagram showing a heating element provided on one side (front side) of the heater substrate and a pattern for forming a power supply path for the heating element. It is a plane schematic diagram of the other surface side (front surface side) of the heater substrate. It is a graph which shows the relationship between heating time and belt temperature. It is a graph which shows the relationship of the elapsed time and belt temperature in control in a reference example . 5 is a control flowchart (No. 1) of the fixing device in the reference example . 6 is a control flowchart (No. 2) of the fixing device in the reference example . 6 is a graph showing the relationship between the elapsed time from the start of power supply to the heater of the fixing device and the temperature of the pressure roller in the experiment in Example 1 . It is a schematic diagram explaining the form of thermal expansion of the paper passing part and the non-paper passing part of the pressure roller. 6 is a control flowchart (No. 1) of the fixing device according to the first exemplary embodiment . 3 is a control flowchart ( No. 2) of the fixing device according to the first exemplary embodiment . 6 is a control flowchart (No. 3) of the fixing device according to the first exemplary embodiment. FIG. 6 is a configuration explanatory diagram of a fixing device according to a second embodiment .

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, although an Example is an example of embodiment which can apply this invention, this invention is not limited only to an Example and various deformation | transformation are possible within the range of the thought of this invention.

《Reference example》
[Image forming unit]
Figure 3 is a picture image heating apparatus is a configuration schematic diagram of an example of an image forming apparatus as a fixing apparatus for heating pressure fixing an unfixed image. In this image forming apparatus 1, a toner image corresponding to image information input from a host device 23 (FIG. 1) to a control unit (control circuit unit) 24 is converted into a sheet-like recording material (recording medium: hereinafter) using electrophotographic technology. This is a color printer that can be formed on P).

  An image forming unit 2 includes four image forming stations 3Y, 3M, 3C, and 3K for forming an image on the paper P. The paper P is fed from a paper feed cassette 19 or 20 or a manual feed tray (multi-feed tray) 21 and is transported by a transport mechanism 22 including a registration roller pair 22a.

  Each image forming station includes a rotating drum type photoreceptor 4 as an image carrier, a charging member 5, a laser scanner 6, a developing device 7, a primary charging blade 8, and a photoreceptor cleaner 9. The image forming stations 3Y, 3M, 3C, and 3K form yellow (Y), magenta (M), cyan (C), and black (K) toner images, respectively.

  Further, the image forming unit 2 includes an intermediate transfer unit 10, and a secondary transfer roller transfers a composite toner image, which is primarily transferred by superimposing each color toner image on the intermediate transfer belt 11 from the image forming stations 3Y, 3M, 3C, 3K. 12 is batch-transferred to the paper P by 12. The registration roller pair 22a temporarily receives the leading end of the paper P and straightens it when the paper P is skewed. Then, in synchronization with the toner image on the intermediate transfer belt 11, the paper P is fed between the intermediate transfer belt 11 and the secondary transfer roller 12. Since the above-described operation of the image forming unit 2 and the color image forming process are well known, detailed description thereof will be omitted.

  The sheet P on which the unfixed toner image is secondarily transferred in the image forming unit 2 is sent to the fixing device 40, where the toner image is heated and pressed and fixed as a fixed image. The paper P exiting the fixing device 40 is routed to the first path 14 side or the second path 15 side by the flapper 13 according to the mode selection in advance. The paper P introduced into the first path 14 is discharged to the face down tray 16 on the upper surface side of the apparatus. The paper P introduced into the second path 15 is discharged to the face-up tray 17 on the side surface of the apparatus.

  In the double-sided image forming mode, the sheet P on which the first side image has been formed exiting the fixing device 40 is once introduced into the first path 14, then switched back and introduced into the third path 18. Then, the sheet is conveyed again through the conveyance mechanism 22 while being reversed with respect to the image forming unit 2.

[Fixing device]
(1) Schematic Description of Device Configuration FIG. 1 is an enlarged cross-sectional right side schematic view of a main part of a fixing device 40 in this reference example and a block diagram of a control system. FIG. 2A is a schematic front view of a middle part of the main part of the fixing device 40 omitted.

Here, with respect to the constant Chakusochi 40 or its components, it is a surface viewed fixing device 40 from the paper inlet side to the front side, the rear side surface on the opposite side (sheet outlet side). Left and right are left (one end side) or right (the other end side) when the fixing device 40 is viewed from the front side. In the fixing device 40 of this reference example , the right side is the driving side and the left side is the non-driving side.

  The upstream side and the downstream side are the upstream side and the downstream side with respect to the paper transport direction X. The longitudinal direction (width direction) and the paper width direction are directions substantially parallel to a direction orthogonal to the transport direction X of the paper P on the paper transport path surface. The short side direction is a direction substantially parallel to the conveyance direction X of the paper P on the paper conveyance path surface.

The fixing device 40 is a belt (film) heating type, tension-less type on-demand fixing device, and is a horizontally long device having a longitudinal direction in the left-right direction. The fixing device 40 is roughly divided into a belt unit 41 including an endless belt (film) 43 having flexibility as a heating rotator, and a pressure roller (elasticity) having heat resistance and elasticity as a pressure rotator. Roller) 42.

  The belt unit 41 includes an endless belt 43, a heater 44 as a heating body (heating source), a heater holder 45 as a holding member for fixing and holding the heater 44, a pressure stay 46, and end members on both left and right end sides ( It is an assembly such as a fixing flange 47 (L, R).

The belt 43 is a member that transfers heat to the paper P, and is a cylindrical (cylindrical, endless) member that is long in the left-right direction and has overall flexibility. FIG. 2B is a schematic diagram showing the layer structure of the belt 43 in this reference example . The belt 43 includes a cylindrical base layer 43a, an elastic layer 43b formed on the outer peripheral surface of the base layer 43a, and a release layer 43c as a surface layer formed on the outer peripheral surface of the elastic layer 43b. And a four-layer composite structure with an inner surface coating layer 43d formed on the inner peripheral surface of the base material layer 43a.

For the base material layer 43a, a heat resistant material having a thickness of 100 μm or less, preferably 50 μm or less and 20 μm or more can be used in order to improve the quick start property. For example, a metal belt such as SUS or nickel can be used. In this reference example , a cylindrical nickel metal belt having a thickness of 30 μm and a diameter of 25 mm was used.

The elastic layer 43b can use a rubber material having a thickness of 1000 μm or less, preferably 500 μm or less in order to reduce the heat capacity and improve the quick start property. For example, silicone rubber, fluorine rubber and the like can be mentioned. In this reference example , silicone rubber having a rubber hardness of 10 degrees (JIS-A), a thermal conductivity of 1.3 W / m · K, and a thickness of 300 μm was used.

For the release layer 43c, a fluororesin material having a thickness of 100 μm or less, preferably 20 to 70 μm can be used. For example, examples of the fluororesin layer include PTFE, FEP, PFA, and the like. In this reference example , a 30 μm thick PFA tube was used.

As the inner surface coat layer 43d, a resin layer having heat resistance can be used because it is in contact with the heater 44. An example is engineering plastic. Specific examples include polyimide, polyimide amide, PEEK, and polytetrafluoroethylene resin (PTFE). Moreover, tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), and the like can be given. In this reference example , polyimide was used to form a coloring layer, and then a raw material solution in a varnish state was applied to the substrate and baked to form a 10 μm polyimide inner layer.

  The heater 44, the heater holder 45, and the pressure stay 46 are all members that are long in the left-right direction. The belt 43 is loosely fitted around the assembly of the heater holder 45 and the pressure stay 46 that holds the heater 44 fixedly. The terminal member 47 (L, R) is attached to one end and the other end of the pressure stay 46 on one end and the other end of the belt 43.

The heater 44 is a ceramic heater in this reference example . The heater 44 is basically composed of an elongated and thin plate-like ceramic substrate and a heating element (an energization heating resistor layer) that receives heat and is provided on the surface of the substrate. It is a low heat capacity heater that raises the temperature with a steep rise characteristic. A more specific structure of the heater 44 will be described in detail in section (3).

  The heater holder 45 is a molded product made of heat-resistant resin, and a heater insertion groove is formed along the longitudinal direction at the center of the outer surface. The heater 44 is fitted and fixed in the groove. The heater holder 45 holds the heater 44 and functions as a rotation guide member (backup member) of the belt 43 that is externally fitted to the heater holder 45 and the pressure stay 46.

The pressure stay 46 is a member having rigidity, and is a member for imparting longitudinal strength to the heater holder 45 by pressing it against the back side of the resin heater holder 45 and for correcting the heater holder 45. In this reference example , the pressure stay 46 is a U-shaped or U-shaped metal mold member having a downward cross section.

  Each of the terminal members 47 (L, R) is a heat-resistant resin-molded product having a symmetrical shape, restricting movement (thrust movement) along the length of the heater holder during rotation of the belt 43 and the inner peripheral surface of the belt end. To regulate the shape of the belt in the circumferential direction.

  That is, the terminal member 47 (L, R) has a seat portion 47 a for receiving the belt end surface as a first restricting portion that restricts the thrust movement of the belt 43. Further, it has an inner surface guide portion 47b as a second restricting portion which is fitted into the belt end portion and guides the inner surface of the belt end portion. The inner surface guide portion 47b is configured so that the belt 43 maintains the substantially elliptical shape that has a substantially elliptical cross-sectional shape when the belt 43 rotates following the rotation of the pressure roller 42 as a drive rotator. Guide the inner surface of the end.

  The pressure roller 42 includes a cored bar (roller base: pipe material) 42a such as SUS or iron, an elastic material layer 42b formed concentrically around the cored bar in a roller shape, and a separation covering the outer peripheral surface thereof. An elastic roller having a composite layer structure including a mold layer (surface layer) 42c. The elastic material layer 42b is, for example, a heat-resistant rubber such as silicone rubber or fluorine rubber, or a foam of silicone rubber.

The pressure roller 42 of this reference example is provided with a silicone rubber layer 42b having a thickness of 5 mm and a volume expansion coefficient of 1.05 × 10 ⁻³ ° C. ⁻¹ on a SUS roller-shaped cored bar 42a having an outer diameter of 20 mm. Thus, the outer diameter is 30 mm. In the pressure roller 42, the rotation center shaft portions 42d on the left and right ends are respectively provided with bearing members (bearings) 49 (L, R) between the left and right side plates 48 (L, R) of the fixing device frame (frame). It is held so as to be able to rotate.

  A drive gear G is disposed concentrically and integrally on the right shaft portion 42d on the drive side. The driving force of the driving means (motor) M controlled by the control unit 24 is transmitted to the gear G through a power transmission mechanism (not shown). As a result, the pressure roller 42 is driven to rotate at a predetermined peripheral speed in the counterclockwise direction of the arrow R42 in FIG.

  On the other hand, the belt unit 41 is arranged on the upper side of the pressure roller 42 so as to be substantially parallel to the pressure roller 42 with the heater arrangement portion side of the heater holder 45 facing downward, and left and right side plates 48 (L, R). It is arranged in between. More specifically, vertical guide groove portions 47d provided in the left and right terminal members 47 (L, R) of the belt unit 41 are provided in the left and right side plates 48 (L, R), respectively. 48a is engaged.

  Accordingly, the left and right terminal members 47 (L, R) are held so as to be slidable in the vertical direction with respect to the left and right side plates 48 (L, R), respectively. That is, the belt unit 41 is held so as to be slidable in the vertical direction with respect to the left and right side plates 48 (L, R). The heater arrangement portion of the heater holder 45 of the belt unit 41 faces the pressure roller 42 with the belt 43 interposed therebetween.

  Then, the pressure receiving portions 47c of the left and right terminal members 47 (L, R) are pressurized with a predetermined pressing force by the left and right pressurizing mechanisms 50 (L, R), respectively. That is, the belt unit 41 is pressed against the pressure roller 42 with a predetermined pressing force. As a result, the heater arrangement portion of the heater holder 45 and the pressure roller 42 are pressed against each other against the elasticity of the elastic material layer 42b across the belt 43, and the belt 43 is pressed between the pressure roller 42 and the pressure roller 42. A nip portion N having a predetermined width is formed in the short direction.

The left and right pressure mechanisms 50 (L, R) are mechanisms having, for example, pressure springs, pressure cams, and the like. The heater 44 is positioned in the heater holder longitudinal direction at a portion corresponding to the nip portion N of the heater holder 45. In the fixing device 40 of this reference example , the heater 44 and the heater holder 45 are nip forming members that come into contact with the inner surface of the belt 43. The pressure roller 42 forms the nip portion N together with the nip forming members 44 and 45 via the belt 43. As described above, the heater 44 is provided inside the belt 43, and the heater 44 and the pressure roller 42 are pressed against each other with the belt 43 interposed therebetween, so that a nip portion N is formed.

(2) Fixing operation The fixing operation of the fixing device 40 is as follows. The control unit 24 activates the driving unit M at a predetermined control timing. A rotational driving force is transmitted from the driving means M to the pressure roller 42 via a rotational driving transmission system (not shown). Thereby, the pressure roller 42 is rotationally driven at a predetermined speed in the counterclockwise direction of the arrow R42.

  When the pressure roller 42 is driven to rotate, rotational torque acts on the belt 43 at the nip portion N due to frictional force with the pressure roller 42. As a result, the belt 43 slides while the inner surface thereof is in close contact with the surface of the heater 44 and the outer circumference of the heater holder 45 and the pressure stay 46 is rotated at a speed substantially corresponding to the speed of the pressure roller 42 in the clockwise direction of the arrow R43. Followed rotation. A semi-solid lubricant is applied to the inner surface of the belt 43 to ensure the slidability between the outer surface of the heater 44 and the heater holder 45 and the inner surface of the belt 43 at the nip portion N.

  As described above, the pressure roller 42 is a driving rotating body that drives the belt 43 and forms the nip portion N in cooperation with the belt 43.

  Further, the control unit 24 starts energizing the heater 44 from the power supply unit (power supply unit) 25. Power is supplied from the power supply unit 25 to the heater 44 through the electrical connectors 51 (L, R) on one end side and the other end side mounted on the left and right portions of the belt unit 41. This energization causes the heater 44 to rapidly rise in temperature. The temperature rise is detected by the thermistor TH (1-5) provided on the back side (upper surface) of the heater 44. The thermistor TH is connected to the control unit 24 via the A / D converter 26. The belt 43 is heated at the nip portion N when the heater 44 generates heat when energized.

  The control unit 24 samples the output from the thermistor TH at a predetermined cycle, and is configured to reflect the temperature information thus obtained in the temperature control. That is, the control unit 24 determines the temperature control content of the heater 44 based on the output of the thermistor TH, and the temperature of the portion corresponding to the sheet passing portion of the heater 44 is set to the target temperature (predetermined setting) by the power supply unit 25. Temperature), the power supply to the heater 44 is controlled.

  In the control state of the fixing device 40 described above, the paper P carrying the unfixed toner image is conveyed from the image forming unit 2 side to the fixing device 40 side and introduced into the nip portion N. The heat of the heater 44 is applied via the belt 43 while the paper P is nipped and conveyed at the nip portion N. The unfixed toner image is fused and fixed as a fixed image on the surface of the paper P by the heat of the heater 44 and the pressure of the nip portion N. The sheet P that has exited the nip portion N is separated from the belt 43 by the curvature, and is discharged and conveyed from the fixing device 40. When the printing operation is completed, the control unit 40 stops power supply from the power supply unit 25 to the heater 44 and stops the driving unit M according to an instruction to end the fixing operation.

  In FIG. 2A, A is the maximum heat generation area width of the heater 44. B is the maximum sheet passing width of the sheet P that can be passed through the fixing device 40, and is the same width as the maximum heating area width A of the heater 44 or a slightly smaller width. The full length area (= the length of the pressure roller 42) of the nip portion N formed by the belt 43 and the pressure roller 42 is a width that is slightly larger than the maximum heat generation area width A of the heater 44.

In the fixing device 40 of this reference example , the conveyance of the paper P is performed by so-called central reference conveyance centered on the paper width. In other words, the paper P of any width size that can be used in the apparatus passes through the central portion in the longitudinal direction of the belt 43 (the central portion of the maximum heat generation area width A of the heater 44). become.

(3) Heater FIG. 4A is an enlarged schematic cross-sectional view of the heater 44, and FIG. 4B is a heating element 44b (1-5) provided on one side (front side) of the heater substrate 44a and its heat generation. It is the schematic diagram which showed the formation pattern of the electric power feeding path 44c with respect to a body.

  The heater 44 is a ceramic heater. The heater 44 includes an elongated thin plate-like heater substrate 44a, a heating element 44b (1-5) formed along the length on one side of the heater substrate 44a, a power supply path 44c for the heating element 44b, And a surface protective layer 44d formed thereon. Moreover, it has the thermistor TH (1-5) as a heater temperature detection member (contact-type thermometer) arrange | positioned by the other surface side (back surface side) of the heater board | substrate 44a.

In this reference example , the heater 44 has the surface protective layer 44d side facing the inner surface of the belt 43 at the nip portion N, and is fitted in the groove portion of the heater holder 45 with the surface protective layer 44d side facing outside and held by the heater holder 45. ing.

The heater substrate 44a is a ceramic material such as alumina or aluminum nitride. The heating element 44b is a layer (heating resistor layer) obtained by patterning and heating an energization heating resistor material such as Ag / Pd (silver palladium), Ta ₂ N, or RuO ₂ by screen printing or the like. The power supply path 44c is a layer (conductive layer) obtained by patterning a conductive material such as Ag paste by screen printing or the like and baking it. The surface protective layer 44d is a layer (electrical insulating layer) obtained by patterning and baking a heat-resistant and electrically insulating material such as heat-resistant glass by screen printing or the like.

The heating elements 44b are arranged side by side along the longitudinal direction of the belt 43, and are individually heated to generate a plurality of heating elements (heating elements: hereinafter referred to as individual heating elements) 44b-1, 44b- 2, 44b-3, 44b-4, and 44b-5. In the present reference example , as shown in FIG. 4B, the heating element 44b has five first to fifth individual heating elements 44b-1, 44b-2, 44b from one end side to the other end side in the longitudinal direction. -3, 44b-4, 44b-5.

  Adjacent individual heating elements are separated by an insulating gap α having a width of about 1 mm. The insulating gaps α are formed obliquely with respect to the transport direction X of the paper P, and the heat generation areas between the individual heating elements are overlapped in the paper transport direction X. Thereby, the continuity of the heat generating area between the heat generating elements in the paper transport direction X is ensured.

In this reference example , the heat generation width in the longitudinal direction of the first to fifth individual heating elements 44b-1, 44b-2, 44b-3, 44b-4, 44b-5 is as shown in Table 1. In addition, the heat generation width of each individual heating element is the longitudinal dimension at the center in the short direction of each individual heating element.

The power supply path 44c for the heating element 44b can control the energization and the power supply to each individual heating element independently, and heat the entire length of the heating area of each individual heating element with a predetermined control power. It is a possible electric circuit pattern. In this reference example , the power supply unit 25 is controlled by the control unit 24, and the gap between the common electrode 44 c-6 on one end side of the heater 44 and the individual electrodes 44 c-1 to 44 c-5 on the other end side. In step 1, the power supply and the amount of supplied power are controlled independently.

  The common electrode 44c-6 and the power supply unit 25 are electrically connected via the lead wire 25a and the electric connector 51L on one end side. The individual electrodes 44c-1 to 44c-5 and the power supply unit 25 are electrically connected to each other through the lead wire 25a and the electric connector 51L on the other end side.

  Specifically, by supplying power between the common electrode 44c-6 and the first individual electrode 44c-1, the entire length of the heat generation area of the first individual heating element 44b-1 can be supplied. It generates heat at a heat generation amount corresponding to. By supplying power between the common electrode 44c-6 and the second individual electrode 44c-2, the entire heat generation area of the second individual heating element 44b-2 corresponds to the amount of power supplied. Generate heat. By supplying power between the common electrode 44c-6 and the third individual electrode 44c-3, the entire heat generation area of the third individual heating element 44b-3 corresponds to the amount of power supplied. Generate heat.

  Further, since the power is supplied between the common electrode 44c-6 and the fourth individual electrode 44c-4, the full length region of the heat generation region of the fourth individual heating element 44b-4 corresponds to the amount of power supplied. It generates heat with a calorific value. By supplying electric power between the common electrode 44c-6 and the fifth individual electrode 44c-5, the total heat generation area of the fifth individual heating element 44b-5 corresponds to the amount of power supplied. Generate heat.

  In FIG. 4B, S is a center paper passing reference line (virtual line) of the paper P. The center sheet passing reference line S corresponds to the substantially central portion of the heat generation width of the third individual heating element 44b-3. The heat generation width of the heat generation area of the third individual heating element 44b-3 substantially corresponds to the vertical feed width (A5 vertical size (A5R): 146 mm) of A5 size paper.

  The combined heat generation area of the second, third, and fourth individual heating elements 44b-2, 44b-3, and 44b-4 is the vertical feed width (A4 vertical size (A4R): 210 mm) of A4 size paper. ). The combined heat generation area of the first to fifth individual heating elements 44b-1 to 44b-5 substantially corresponds to the lateral feed width (A4 horizontal size: 297 mm) of A4 size paper.

In this reference example , the maximum width size (maximum sheet passing width) of the paper P that can be passed (introduced) into the fixing device 40 is the A4 horizontal size. The total heat generation width including the heat generation areas of the first to fifth individual heating elements 44b-1 to 44b-5 is the maximum heat generation area width A of the heater 44. It almost corresponds to the A4 horizontal size which is the width size.

In this reference example, as described later, the sheet passing portion in accordance with the width size of the size of the paper P to be fed to the fixing device 40 separately heating element corresponding to (a recording material passing portion) and the non-sheet passing portion (recording This is a control configuration for selectively switching power supply and power supply to the individual heating elements corresponding to the material non-passing portion.

  As shown in FIG. 5, the thermistor TH contacts the heater substrate 44a at positions corresponding to the first to fifth individual heating elements 44b-1 to 44b-5 on the other surface side of the heater substrate 44a. Thus, a total of five first to fifth (TH1 to TH5) are arranged.

  The first to fifth thermistors TH1 to TH5 detect the temperatures of the portions corresponding to the first to fifth individual heating elements 44b-1 to 44b-5 of the heater 44, respectively, and detect the temperature detection information (detection results). ) Is fed back to the temperature control means unit (temperature control function unit) of the control unit 24. Based on the temperature detection information of each of the thermistors TH1 to TH5, the control unit 24 controls the input power to each individual heating element so as to reach the target temperature for each heater portion where the corresponding individual heating element exists.

(4) Relationship between Belt Temperature and Rise Time Next, an experiment was conducted on the relationship between the temperature of the belt 43 and the time until the target temperature was reached. In this experiment, a fixing device 40 as shown in FIGS. As operating conditions, the belt rotation speed is 248 mm / s, the applied pressure is 314 N (32 kgf) in total pressure, and the electric power supplied to the heater 44 is the sum of the five individual heating elements 44 b-1 to 44 b-5. 800W. In addition, the ultimate target temperature was set to 180 ° C. (predetermined first temperature) at the heater temperature (belt back surface temperature: hereinafter referred to as belt temperature) detected by the thermistors TH1 to TH5. In this reference example , the belt temperature of 180 ° C. is the image fixing temperature.

  FIG. 6 shows the relationship between the elapsed time from the start of power supply and the belt temperature in this experiment. Thus, it was confirmed that when the belt temperature was 100 ° C., the target temperature (180 ° C.) was reached in 5 seconds, and when it was 130 ° C., it reached in 3 seconds.

(5) Relationship between the auxiliary heating state at the end and the image gloss after fixing Next, an experiment was conducted on the relationship between the auxiliary heating state at the end and the image gloss after fixing. Here, the end portion refers to a non-sheet passing portion when a sheet (small size sheet) having a smaller width than a sheet having a maximum sheet passing width B (maximum size sheet) in the maximum heat generation area width A of the heater 44 is passed. It is a heater part or a belt part corresponding to. When the sheet is conveyed by the center reference conveyance, a non-sheet passing portion having a width of (maximum sheet passing width B−small size sheet passing width) / 2 is generated on both sides of the small size sheet passing portion. When the sheet is a maximum size sheet, the heater 44 does not have a non-sheet passing portion.

  The auxiliary heating at the end is as follows. That is, when small-size paper is passed, power is supplied to the individual heating elements corresponding to the paper passing portion, and the temperature of the heater portion (belt portion) corresponding to the paper passing portion is heated to a predetermined target temperature. Then, the heater part (belt part) corresponding to the non-sheet passing part is also controlled at a predetermined temperature (the first temperature is lower than the first temperature) by controlling the individual heating elements corresponding to the non-sheet passing part. Heating to a predetermined second temperature).

  The image gloss after fixing corresponds to the passing portion of the small size paper in the large size paper when the large size paper having a larger width is passed after passing the small size paper. This is an image gloss state between the fixed image portion and the fixed image portion corresponding to the non-sheet passing portion.

  In this experiment, a fixing device 40 as shown in FIGS. As operating conditions, the belt rotation speed was 248 mm / s, the applied pressure was 314 N (32 kgf) in total pressure, and the target temperature of the belt 43 was 180 ° C.

  Next, the energized state of the heater 44 will be described. In this experiment, first, up to a target temperature of 180 ° C., 800 W in total was applied to the first to fifth individual heating elements 44b-1 to 44b-5 to heat the belt 43. That is, the full length area of the maximum heat generation area width A of the heater 44 (area corresponding to the maximum sheet passing width of the belt 43) was raised to 180 ° C.

  Thereafter, when a printing operation is performed using a 148 mm-wide sheet (A5 vertical size), which is a small-sized sheet, 400 W of power is applied to the third heating element 44b-3 located in the sheet passing portion of the sheet. . Then, the temperature of the heater portion (belt portion) corresponding to the heat generation width of the third heating element 44b-3 is adjusted at 180 ° C.

  On the other hand, power supply to the first, second, fourth, and fifth heating elements 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion of the sheet is the following three. In each case, the image gloss after fixing in each case was examined.

  Case 1: This is a case where the power input to the individual heating elements 44b-1, 44b-2, 44b-4, 44b-5 corresponding to the non-sheet passing portion is set to 0 W (when power is not applied).

  Case 2: The case where the power input to the heating elements 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion is 25 W, respectively.

  Case 3: The case where the power input to the heating elements 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion is 50 W, respectively.

The evaluation method is as described below. First, A5 size paper (148 mm × 210 mm) of CS-680 (manufactured by Nippon Paper Industries Co., Ltd.) as a small size paper is continuously fed in a direction in which the longitudinal direction is 148 mm (A5 vertical size). did. After that, as a large size paper, CS-680 (manufactured by Nippon Paper Industries Co., Ltd.) A4 size paper (210 mm × 297 mm) on which 1.2 mg / cm ² of unfixed toner is placed is 297 mm (A4 horizontal size) in the longitudinal direction. ).

Measure the 60 ^o gloss of the obtained image after fixing using a handy gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd.), and the gloss values at the center and edge in the paper width direction are comparable. The heating time of the edge part required until it became was compared. The results are shown in Table 2. Note that the central portion and the end portion in the paper width direction are a portion corresponding to the paper passing portion of the previous small size paper and a portion corresponding to the non-paper passing portion in the large size paper.

  FIG. 7 is a graph showing the heating condition of the end portion (non-sheet passing portion) and the temperature transition of the belt 43 after reaching the target temperature. The central portion (the belt portion corresponding to the passing portion of the small paper) is constant at 180 ° C., and the non-passing portion is applied to the individual heating element corresponding to the non-passing portion, The constant temperature was different.

  When power is not applied to the individual heating elements in the non-sheet-passing portion, the temperature at the belt end decreases to 25 ° C., which is room temperature, 100 ° C. when 25 W power is applied, and 130 when 50 W power is applied. It became constant at ℃. Since these constant temperatures are different, when no power is applied, the time required to raise the non-sheet passing portion to the target temperature of 180 ° C. is 10 seconds, and 25 W and 50 W are applied to assist heating. In this case, it becomes 5 seconds and 3 seconds, respectively. In other words, it was confirmed that when the non-sheet passing portion was auxiliary heated, the time required for raising the temperature of the non-sheet passing portion to the target temperature was shortened.

  From the viewpoint of productivity when switching the paper size, the required time is preferably about 3 seconds. Therefore, it was confirmed that the target time required for switching the size was reached by supplying 50 W of power to the individual heating elements in the non-sheet passing portion.

(6) Paper Size Switching and Auxiliary Heating Control FIGS. 8A and 8B are flowcharts of fixing device operation control including paper size switching and auxiliary heating control in this reference example . Hereinafter, each step will be described. This fixing device operation control is executed by the control unit 24.

  S100: The image forming operation of the image forming unit 2 is started based on the image formation start signal.

  S101: For the fixing device 40, rotation driving of the pressure roller 42 is started at a predetermined control timing. In addition, energization of all the first to fifth individual heating elements 44b-1 to 44b-5 is started (longitudinal area heater ON), and the full length area of the maximum heating area width A of the heater 44 is 180 ° C. (first Temperature).

In this reference example , 400 W of electric power is applied to the third individual heating element 44b-3 at the longitudinal center. The other first, second, fourth, and fifth individual heating elements 43b-1, 43b-2, 43b-4, and 43b-5 are each applied with 100 W of power. And each temperature control system including the first to fifth thermistors TH1 to TH5 is adjusted so that the temperature of the heater portion (belt portion) corresponding to each individual heating element is raised to 180 ° C. The power supplied to the individual heating elements is individually controlled.

  S102: The size of the paper to be used is detected. The paper size is detected by, for example, inputting paper information used from the host device 23 to the control unit 24. Alternatively, paper information selected and specified by the user is input from the operation unit 27 of the image forming apparatus 1 to the control unit 24. Alternatively, detection size information is input to the control unit 24 from means (not shown) for automatically detecting the paper size fed from the paper feed unit.

In this reference example , for convenience, there are three types of paper widths that are used by switching the size of the apparatus: A5 vertical size (width 148 mm), A4 vertical size (210 mm), and A4 horizontal size (297 mm). The A4 horizontal size is the large size paper width, and the A5 vertical size and the A4 vertical size are each the small size paper width with respect to the large size paper width of 4 horizontal sizes.

If the paper size to be used is A5 vertical size, the process proceeds to step S103. If the paper size is other than that, the process proceeds to the flowchart of FIG. 8B. S103: If the paper size is A5 vertical size, the third individual heating element layer corresponding to the paper passing portion of the paper The electric power of 400 W is applied to 44b-3, and the temperature is adjusted so that the belt temperature of the sheet passing portion is maintained at the target temperature of 180 ° C.

  A power of 50 W is applied to each of the first, second, fourth, and fifth individual heating element layers 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion. Thus, the power control is performed, and the belt portion corresponding to the non-sheet passing portion is auxiliary heated.

  S104: In the control state of the fixing device 40, the passing of the A5 portrait paper and the fixing process are started.

  S105: Paper size switching during the movement of the image forming apparatus is monitored.

  S106: If the paper size continues to be A5 vertical size, the process proceeds to step S108. When the paper size is switched to the A4 vertical size, the process proceeds to step S207. When the paper size is switched to the A4 landscape size, the process proceeds to step S307.

  S108: If the paper size continues to be A5 vertical size, the paper passing and fixing process is continued.

  S109: The sheet passing and fixing process for a predetermined set number of sheets is completed.

  S110: Energization to all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

S207: When the size is switched to A4 length in step S106, the second, third, and fourth individual heating element layers 44b-2, 44b-3, and 44b- corresponding to the sheet passing portion of the sheet are used. A predetermined power is applied to 4. Then, the temperature is adjusted so that the belt temperature of the sheet passing portion is maintained at the target temperature of 180 ° C. In this reference example , 400 W of power is applied to the third individual heating element layer 44b-3, and 100 W of power is applied to the second and fourth individual heating element layers 44b-2 and 44b-4, respectively. The

  The first and fifth individual heating element layers 44b-1 and 44b-5 corresponding to the non-sheet passing portion are subjected to power control so that 50 W of power is applied to each of the first and fifth individual heating element layers 44b-1 and 44b-5. The belt portion to be auxiliary is heated.

  S208: Paper passing and fixing processing are started in the control state of the fixing device 40.

  S209: The predetermined number of sheets to be passed and the fixing process are completed.

  S210: Energization to all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

S307: When the size is switched to the A4 landscape size in step S106, since this sheet is a sheet having the maximum sheet passing width B, the full length area of the maximum heat generating area width A of the heater 44 is raised to 180 ° C. It is adjusted. In this reference example , 400 W of electric power is applied to the third individual heating element 44b-3 at the longitudinal center. The other first, second, fourth, and fifth individual heating elements 43b-1, 43b-2, 43b-4, and 43b-5 are each applied with 100 W of power.

  And each temperature control system including the first to fifth thermistors TH1 to TH5 is adjusted so that the temperature of the heater portion (belt portion) corresponding to each individual heating element is raised to 180 ° C. The power supplied to the individual heating elements is individually controlled.

  S308: The sheet passing and fixing process is started in the control state of the fixing device 40.

  S309: The predetermined number of sheets to be passed and the fixing process are completed.

  S310: Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

  S102: Referring to FIG. 8B, when the paper size is A4 vertical size in step S102 of FIG. 8A, the process proceeds to step S403. In the case of A4 horizontal size, the process proceeds to step S608.

S403: In the case of A4 portrait size, predetermined power is supplied to the second, third, and fourth individual heating element layers 44b-2, 44b-3, and 44b-4 corresponding to the sheet passing portion of the sheet. The applied temperature is adjusted so that the belt temperature of the sheet passing portion is maintained at the target temperature of 180 ° C. In this reference example , 400 W of power is applied to the third individual heating element layer 44b-3, and 100 W of power is applied to the second and fourth individual heating element layers 44b-2 and 44b-4, respectively. The

  The first and fifth individual heating element layers 44b-1 and 44b-5 corresponding to the non-sheet-passing portion are subjected to power control so that 50 W of power is applied to each of the first and fifth individual heating element layers 44b-1 and 44b-5. The part is auxiliary heated.

  S404: In the control state of the fixing device 40, A4 portrait size paper passing and fixing processing are started.

  S405: Paper size switching during the movement of the image forming apparatus is monitored.

  S406: If the paper size continues to be A4 vertical size, the process proceeds to step S408. If the paper size is switched to the A4 landscape size, the process proceeds to step S507.

  S408: If the paper size continues to be A4 vertical size, the paper passing and fixing process is continued.

  S409: Passing the predetermined number of sheets and fixing processing are completed.

  S410: Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

S507: When the size is switched to the A4 landscape size in step S106, since this sheet is a sheet having the maximum sheet passing width B, the full length area of the maximum heat generating area width A of the heater 44 is raised to 180 ° C. It is adjusted. In this reference example , 400 W of electric power is applied to the third individual heating element 44b-3 at the longitudinal center. The other first, second, fourth, and fifth individual heating elements 43b-1, 43b-2, 43b-4, and 43b-5 are each applied with 100 W of power.

  And each temperature control system including the first to fifth thermistors TH1 to TH5 is adjusted so that the temperature of the heater portion (belt portion) corresponding to each individual heating element is raised to 180 ° C. The power supplied to the individual heating elements is individually controlled.

  S508: Paper passing and fixing processing are started in the control state of the fixing device 40.

  S509: The passing of the predetermined number of sheets and the fixing process are completed.

  S510: Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

  S608: If the sheet size is A4 landscape size in step S102 of FIG. 8A, the A4 landscape size paper passing and fixing process is started in the control state of the fixing device 40 in step S101.

  S609: The predetermined number of sheets to be passed and the fixing process are completed.

  S610: Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

  As shown in FIGS. 8A and 8B, the required time for switching the paper size when the fixing device 40 is controlled is summarized in Table 3.

As described above, it was confirmed that the required time for switching the paper size was 3 seconds by using the control of this reference example .

(7) Comparison with Comparative Example Next, the reference example and the comparative example were compared. As operating conditions, the belt rotational speed was 248 mm / s, the applied pressure was 314 N (32 kgf) in total pressure, and the target temperature of the belt was 180 ° C.

As an evaluation method, 50 sheets of A5 size paper (148 mm × 210 mm) of CS-680 (manufactured by Nippon Paper Industries Co., Ltd.) are sent as small size paper in a direction in which the longitudinal direction is 148 mm (A5 vertical size). Paper. After that, as a large size paper, CS-680 (manufactured by Nippon Paper Industries Co., Ltd.) A4 size paper (210 mm × 297 mm) on which 1.2 mg / cm ² of unfixed toner is placed is 297 mm (A4 horizontal size) in the longitudinal direction. ).

The evaluation, handy glossmeter measures 60 ^o gloss by using (Nippon Denshoku Industries Co., Ltd.), needed until the gloss value of the center and the ends of the sheet width direction is to the same extent The heating time at the end was compared.

  The central portion and the end portion in the paper width direction are a portion corresponding to the paper passing portion of the previous small size paper and a portion corresponding to the non-paper passing portion in the large size paper.

Fixing device of comparative example 1: In the fixing device 40 of this reference example , a heater comprising a single heating element having a full heat generation area width A as a heater 44 is used as the heater 44, and a cooling fan (non-sheet passing portion) is provided at the end. The fixing device is provided with a cooling fan. When the temperature of the non-sheet passing portion is increased by continuous printing of small size paper, the belt is cooled by a cooling fan until the temperature is lowered to a predetermined temperature.

Fixing device of comparative example 2: In fixing device 40 of this reference example , when small-size paper is passed, control is performed so that power is not supplied to the individual heating elements corresponding to the non-sheet passing portion. That is, in the fixing device 40 of this reference example , auxiliary heating of the end portion (non-sheet passing portion) is not performed.

Table 4 shows the time required for changing the paper size (time for raising the temperature of the non-sheet passing portion to the target temperature) in the reference example , comparative example 1, and comparative example 2 described above. The center temperature is the temperature of the belt portion corresponding to the paper passing portion when the small-size paper is passed, and the end temperature is the temperature of the belt portion corresponding to the non-paper passing portion.

  In Comparative Example 1, since the long-time cooling is required when the non-sheet passing portion becomes high temperature, the time required for changing the paper size is greatly increased.

  In Comparative Example 2, the non-sheet passing portion is maintained at 25 ° C., but it takes 10 seconds, which is about the same as the initial startup time, in order to raise the temperature from that temperature to the target temperature of 180 ° C. Time has extended.

On the other hand, in the present reference example , the individual heating element corresponding to the non-sheet passing portion has a constant temperature (second temperature) higher than that of the comparative example 2 and lower than the target temperature (first temperature). Temperature). Therefore, it was confirmed that the time required to raise the temperature from the temperature (second temperature) to the target temperature (first temperature) of 180 ° C. was shortened.

  As described above, even when the paper width is changed from the small size paper to the large size paper, it is possible to continue the fixing process without causing an image defect or a paper conveyance defect without causing a decrease in productivity due to downtime or the like. It has become possible.

Example 1
The first embodiment solves the problem caused by the thermal expansion of the pressure roller 42. That is, when small-size paper is passed, heat is transmitted to the portion corresponding to the paper passing portion (recording material passing portion) of the pressure roller through the paper and the temperature rises. On the other hand, in an apparatus configuration that does not generate heat in the heater portion corresponding to the non- sheet passing portion (recording material non-passing portion) , the partial heating corresponding to the non-sheet passing portion of the pressure roller is not performed. Little temperature occurs.

  Since the elastic layer 42b of the pressure roller 42 expands by heating, only the roller portion corresponding to the paper passing portion expands, and the roller portion corresponding to the non-paper passing portion hardly expands. In the fixing device that passes the paper based on the central reference, only the central portion of the paper passing portion of the pressure roller 42 is heated and expanded, and expansion does not occur at both ends of the non-paper passing portion. Therefore, the pressure roller 42 has a shape close to a crown shape whose central portion is thicker than both end portions.

  In general, the pressure roller 42 has a large thickness of the elastic layer 42b in order to obtain a sufficient nip area. The greater the thickness of the elastic layer 42b, the greater the expansion and the more prominent crown shape. If a large-size sheet is passed in this state, the conveyance speed of the central area of the sheet becomes faster than the both end areas. In particular, when a large size of thin paper is passed immediately after passing a large amount of small size paper, the thin large size paper has low paper rigidity and the difference in transport speed between the center and both ends. Paper wrinkles may occur.

  On the other hand, after passing a small size sheet, the temperature difference of the pressure roller 42 becomes small, and it is possible to cope with it by not accepting the next job until the crown shape due to the expansion is settled. However, since the elastic layer 42b of the pressure roller 42 has a large thickness, it has a large volume and a large heat capacity, so that it takes a long time to cool. The long waiting time causes a problem that the productivity of the fixing device is greatly reduced.

Example 1 and Examples 2 and 3 to be described later solve the problems caused by the thermal expansion of the pressure roller 42 as described above. In the first exemplary embodiment , the configuration of the image forming apparatus 1 and the configuration of the fixing device 40 are the same as those of the reference example , and thus the description thereof is omitted.

(1) Relationship between the pressure roller temperature of the paper passing portion and the non-paper passing portion The temperature transition of the pressure roller 42 when the paper is passed by changing the paper size, the longitudinal center of the pressure roller 42 when the small size paper is passed An experiment was conducted on the relationship between the temperature of the part (paper passing part) and the end part (non-paper passing part). In this experiment, the fixing device 40 in the reference example was used. As operating conditions, the belt rotation speed is 248 mm / s, the applied pressure is 314 N (32 kgf) in total pressure, and the electric power supplied to the heater 44 is the sum of the five individual heating elements 44 b-1 to 44 b-5. 800W. Further, the target temperature reached 180 ° C. at the fixing belt back surface temperature (hereinafter referred to as belt temperature) detected by the thermistors T1 to TH5.

  FIG. 9 shows the relationship between the elapsed time from the start of power supply to the heater 44 of the fixing device 40 and the temperature of the pressure roller 42 in this experiment. FIG. 9A shows the temperature transition during the passage of A4 landscape size paper (width 297 mm), which is the maximum size paper. All of the first to fifth individual heating element layers 44b-1 to 44b-5 are energized. The first and fifth individual heating element layers 44b-1, 44b-5 are each 120 W, the second and fourth individual heating element layers 44b-2, 44b-4 are each 80 W, the third individual heating element. The layer 44b-3 is energized with 400W.

  In the case of passing the maximum size sheet, the full length area of the maximum heat generation area A of the heater 44 is a sheet passing portion, and no non-sheet passing portion is generated. In the maximum size sheet passing area, the pressure roller temperature is increased by being heated by the heater 44 via the sheet P and the belt 43. And it reaches about 80 ° C. in about 200 seconds. In this case, since the temperature of the longitudinal center portion and the end portion of the pressure roller 42 is substantially the same, the expansion amount of the pressure roller 42 does not change between the center portion and the end portion.

  Then, as schematically shown in FIG. 10A, the shape of the pressure roller, which was a solid line before the sheet passing, is changed to a broken line by the sheet passing. Although the pressure roller diameter is increased due to thermal expansion, there is no temperature difference between the central portion and the end portion, so that the outer shape is not changed.

  In FIG. 9B, when small-size paper is passed, power is supplied only to the individual heating elements corresponding to the paper passing portion of the paper, and power is not supplied to the individual heating elements corresponding to the non-paper passing portion. It is a temperature transition of the pressure roller longitudinal center part and edge part in the case. Specifically, this is a case where A4 vertical size paper (width 210 mm) is passed. Only the second, third, and fourth individual heating elements 34b-2, 34b-3, and 34b-4 corresponding to the sheet passing portion are energized, and corresponding to the non-sheet passing portion. In this case, the first and fifth individual heating elements 34b-1 and 34b-5 are not energized.

  The third individual heating element 34b-3 has 400W, the second and fourth individual heating elements 34b-2, 34b-4 have 80W, and the first and fifth individual heating elements 34b-1, 34b-5. Each is energized with 0 W.

  In the central portion corresponding to the paper passing portion of the pressure roller 42, the pressure roller temperature is increased by being heated by the heater 44 via the paper P and the belt 43. It reaches about 80 ° C. in about 200 seconds. The end of the pressure roller 42 corresponding to the non-sheet passing portion is not heated by the heater 34, so the temperature does not rise. In this case, since the temperature is greatly different between the central portion and the end portion of the pressure roller 42, the thermal expansion amount of the pressure roller 42 varies between the central portion and the end portion.

Then, as schematically shown in FIG. 10B, the shape of the pressure roller, which was a solid line before passing paper, changes as shown by a broken line by passing paper. When the volume expansion coefficient is 1.05 × 10 ⁻³ ° C.− ¹ , the temperature difference is 65 ° C., and the thickness of the elastic layer 42b is 5 mm, the outer diameter difference is about 0.5 mm. The radius of the central portion of the pressure roller 42 is about 0.5 mm larger than the end portion.

  As a result, in the nip portion N, the central portion in the width direction has a higher sheet conveyance speed than the end portion. Therefore, when a large sheet of thin paper is passed by the pressure roller 42 in this state, the paper wrinkles are caused by the small rigidity of the thin large sheet and the difference in the conveyance speed between the center and both ends. May occur.

  Moreover, since the belt 43 also has the elastic layer 43b, it expand | swells when temperature rises. However, since the elastic layer 43b of the belt 43 has a thickness of 300 μm and the elastic layer 42b of the pressure roller 42 has a thickness of 5 mm, the amount of expansion is about 1/10, so that no paper wrinkle occurs. That is, the pressure roller 42 has a larger expansion amount during heating than the belt 43.

  (C) of FIG. 9 is a temperature transition of the central portion and the end portion of the pressure roller in the case where the individual heating element corresponding to the non-sheet passing portion is also energized when the small size sheet is passed. It is temperature transition. Specifically, as in the case of FIG. 9B, the A4 portrait size paper is passed. In addition to the second, third, and fourth individual heating elements 34b-2, 34b-3, and 34b-4 corresponding to the sheet passing portion of the sheet, the sheet corresponding to the non-sheet passing portion is also supported. This is a case where the first and fifth individual heating elements 34b-1 and 34b-5 are energized.

  In the central portion, which is the paper passing portion of the pressure roller 42, the pressure roller is heated by the heater 44 via the paper P and the belt 43 and the temperature is raised. It reaches about 80 ° C. in about 200 seconds. At the end corresponding to the non-sheet passing portion, the temperature is raised by heating via the belt 43 from the first and fifth individual heating elements 44b-1 and 44b-5 corresponding to the non-sheet passing portion. . The sheet passing area of the pressure roller 42 is heated by the heating element via the sheet P and the belt 43, but the non-sheet passing area is heated only via the belt 43, so the non-sheet passing area is small. The temperature rises with electric power.

  In FIG. 9C, the solid line indicates the temperature transition of the longitudinal center portion of the pressure roller, and the alternate long and short dash line indicates each of the first and fifth individual heating elements 44b-1 and 44b-5 corresponding to the non-sheet passing portion. The temperature transition of the end portion of the pressure roller 42 when 30 W is energized. An alternate long and two short dashes line represents a temperature transition at the end when 60 W is energized to each of the first and fifth individual heating elements 44b-1 and 44b-5 corresponding to the non-sheet passing portion.

When the first and fifth individual heating elements 44 b-1 and 44 b-5 are energized with 60 W, the end portion raises the temperature more than the temperature rise in the center portion. Therefore, the end portion thermally expands to the central portion or more, and as schematically shown in FIG. 10C, the shape of the pressure roller, which was a solid line before passing the paper, changes as shown by the broken line by passing the paper. When the volume expansion coefficient is 1.05 × 10 ⁻³ ° C.− ¹ , the temperature difference is 80 ° C., and the thickness of the elastic layer 42b is 5 mm, the outer diameter difference is about 0.6 mm. As a result, the conveyance speed of the sheet P is slower in the center portion than in the end portion in the nip width direction.

  Therefore, when the large-sized sheet of thin paper is passed by the pressure roller 42 in this state, the rigidity of the large-sized thin sheet is small and the sheet conveyance speed at the center and both ends in the nip width direction is reduced. Due to the difference, the behavior of the trailing edge of the paper becomes unstable. Then, the paper may come into contact with the belt 43 before entering the nip portion, leading to an image defect.

  When 30 W energization is applied to the first and fifth individual heating elements 44b-1 and 44b-5, the temperature of the ends of the first and fifth individual heating elements 44b-1 and 44b-5 rises substantially in the same manner as the temperature rises in the central portion of the pressure roller. In this case, the temperature at the longitudinal center of the pressure roller (the temperature at the part corresponding to the paper passing part) and the temperature at the end (the temperature at the part corresponding to the non-paper passing part) are almost the same. The amount of thermal expansion of the pressure roller does not change between the central portion and the end portion.

  Then, as schematically shown in FIG. 10A, the shape of the pressure roller, which was a solid line before the sheet passing, is changed to a broken line by the sheet passing. Although the diameter of the pressure roller is increased due to thermal expansion, there is no temperature difference between the longitudinal center and the end of the pressure roller, so that the outer shape is not changed. Therefore, when a thin large-size sheet is passed by the pressure roller in this state, neither paper wrinkles nor image defects occur.

(2) Relationship between the temperature difference between the center and end of the pressure roller and paper wrinkles and image defects when passing thin paper Next, the center of the pressure roller 42 (sheet passing portion) and the end (non-sheet passing portion) An experiment was conducted on the relationship between the temperature difference of the paper, the paper wrinkle when passing thin paper, and the image defect. In this experiment, the fixing device 40 in the reference example was used. As operating conditions, the belt rotation speed was 248 mm / s, the applied pressure was 314 N (32 kgf) in total pressure, and the target temperature of the belt 43 was 180 ° C.

  The evaluation method is as described below. First, 150 sheets of A-size paper (210 mm × 297 mm) of CS-680 (manufactured by Nippon Paper Industries Co., Ltd.) are passed as small-size paper in a direction in which the longitudinal direction is 210 mm (A4 vertical size). . Immediately after passing the paper, the thin paper as a large size paper is passed. As the large size paper, 5 sheets of A3 size (297 mm × 420 mm) of OK Prince fine quality 52.3 gsm (manufactured by Oji Paper Co., Ltd.) are passed in such a direction that the longitudinal direction becomes 297 mm (A4 horizontal size). Make paper.

  When the temperature of the pressure roller end portion (non-sheet passing portion) when passing CS-680 as small size paper is changed, five sheets of OK Prince quality 52.3 gsm as large size paper are wrinkled. Check whether or not image defects occur.

  Next, the energized state of the heater 44 will be described. In this experiment, when the above-mentioned small size paper (A4 vertical size) is passed, 80 W is applied to the second and fourth individual heating elements 44b-2 and 444b-4, and 400W is applied to the third individual heating element 44b-3. Energize.

  0 W (no power applied), 10 W, 20 W, 30 W, 40 W, 50 W, and 60 W are applied to the first and fifth individual heating elements 44 b-1 and 44 b-5 corresponding to the non-sheet passing portion, respectively. did. The results are shown in Table 5.

  It was confirmed that when the longitudinal direction (center temperature) − (edge temperature) of the pressure roller 42 exceeded + 20 ° C., paper wrinkles occurred, and when it exceeded −20 ° C., image defects occurred. Therefore, it was confirmed that paper wrinkles and image defects can be prevented by setting the (center temperature)-(edge temperature) of the pressure roller 42 within the range of ± 20 ° C. Therefore, it is desirable to supply power of about 30 W to the first and fifth individual heating elements 44b-1 and 44b-5 corresponding to the non-sheet passing portion of the heater 44.

That is, when the control unit 24 continuously introduces and heats paper having a width smaller than that of the maximum width size, the temperature of the portion corresponding to the recording material non-passing portion of the pressure roller 42 is predetermined. The amount of electric power applied to the individual heating element corresponding to the recording material non-passing portion is controlled so as to be maintained at the third temperature. The third temperature is a temperature that substantially corresponds to the temperature of the portion corresponding to the recording material passage portion of the pressure roller 42. Alternatively, the difference between the third temperature and the temperature of the portion corresponding to the recording material passage portion of the pressure roller 42 is in the range of ± 20 ° C.

(3) heating control 11 size switching the heater of the paper (A), FIG. 11 (B), FIG. 11 (C) is in the first embodiment, the fixing device operations including a heating control of the size switching the heater of the paper It is a flowchart of control. Hereinafter, each step will be described. This fixing device operation control is executed by the control unit 24.

  S100: The image forming operation of the image forming unit 2 is started based on the image formation start signal.

S101: The width size of the paper to be used is detected. The paper width size detection is the same as that described in step S102 of FIG. 8A of the reference example . Also in the first embodiment , the width of the paper used after switching the size is A4 horizontal size (width 297 mm: hereinafter referred to as A4 size), A4 vertical size (width 210 mm), A5 vertical size (width 148 mm). ).

If the paper is A4 landscape size, the process proceeds to step S102. Figure 1 for A4 vertical size
1 (B), the process proceeds to the flowchart of FIG. 11 (C) in the case of A5 vertical size.

  S102: When the paper size is A4 landscape size, the fixing device 40 starts to rotate the pressure roller 42 at a predetermined control timing. In addition, energization of all the first to fifth individual heating elements 44b-1 to 44b-5 is started (longitudinal whole area heater ON), and the full length area of the maximum heating area width A of the heater 44 is raised to 180 ° C. Is done.

In the first embodiment, 400 W of power is applied to the third individual heating element 44b-3 at the longitudinal center. Electric power of 120 W is applied to the first and fifth individual heating elements 44 b-1 and 44 b-5, respectively, and power of 80 W is applied to the second and fourth individual heating elements 44 b-2 and 44 b-4. And each temperature control system including the first to fifth thermistors TH1 to TH5 is adjusted so that the temperature of the heater portion (belt portion) corresponding to each individual heating element is raised to 180 ° C. The power supplied to the individual heating elements is individually controlled.

  S103: In the control state of the fixing device 40, A4 landscape size paper passing and fixing processing are started.

  S104: Paper size switching during the movement of the image forming apparatus is monitored. If the paper size continues to be A4 landscape size, the process proceeds to step S105. If the paper size is switched to A4 vertical size paper, the process proceeds to step S205. When the paper size is switched to A5 vertical size paper, the process proceeds to step S305.

  S105: If the paper size continues to be A4 landscape size, the paper passing and fixing process is continued.

  S108: The predetermined number of sheets to be passed and the fixing process are completed.

  S109: Energization to all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

  S205: The size is switched to A4 vertical size in step S104.

  S206: Regarding the power supply to the heater 44, the third individual heating element 44b-3 is 400 W, the second and fourth individual heating elements 44b-2 and 44b-4 are 80 W, the first and fifth, respectively. A power of 30 W is applied to the individual heating elements 4b-1 and 44b-5.

  Then, the individual heating elements 44b-2 to 44b- are provided by the temperature control system including the thermistors TH2 to TH4 so that the temperature of the heater portion (belt portion) corresponding to the paper passing portion is raised to 180 ° C. The power supplied to 4 is individually controlled. The power supplied to the individual heating elements 4b-1 and 44b-5 corresponding to the non-sheet passing portion is reduced from 120W to 30W, so that the heater portion (belt portion) corresponding to the non-sheet passing portion and the pressure roller portion Temperature rise is suppressed.

  S207: In the control state of the fixing device 40, A4 portrait size paper passing and fixing processing are started.

  S104, S105, S108, S109, S999: Passing and fixing processing of A4 vertical size sheets for a predetermined set number of sheets are completed. Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped. The image forming apparatus 1 is held in a standby state until a start signal for the next image forming job is input.

  S305: The size is switched to A5 vertical size in step S104.

  S306: Regarding power supply to the heater 44, 400 W is applied to the third individual heating element 44b-3 corresponding to the sheet passing portion. A small power of 30 W is applied to each of the first, second, fourth, and 54th individual heating elements 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion.

  The power supply to the individual heating element 44b-3 is controlled by the temperature control system including the thermistor TH3 so that the temperature of the heater portion (belt portion) corresponding to the paper passing portion is raised to 180 ° C. Is done. The power supplied to the individual heating elements 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion is set to a low power of 30 W, so that the heater portion corresponding to the non-sheet passing portion (belt) Part), the temperature rise of the pressure roller part is suppressed.

  S307: In the control state of the fixing device 40, A5 vertical size paper passing and fixing processing are started.

  S104, S105, S108, S109, S999: Passing and fixing processing of A5 vertical size sheets for a predetermined set number of sheets are completed. Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped. The image forming apparatus 1 is held in a standby state until a start signal for the next image forming job is input.

  S101: Referring to FIG. 11B, if the paper size is A4 portrait size in step S101 of FIG. 11A, the process proceeds to step S402.

  S402: When the paper size is A4 vertical size, for the fixing device 40, the fixing device 40 starts to rotate the pressure roller 42 at a predetermined control timing. Regarding the power supply to the heater 44, the third individual heating element 44b-3 is 400 W, the second and fourth individual heating elements 44b-2 and 44b-4 are each 80 W, and the first and fifth individual heating elements. A power of 30 W is applied to each of the bodies 4b-1 and 44b-5.

  Then, the individual heating elements 44b-2 to 44b- are provided by the temperature control system including the thermistors TH2 to TH4 so that the temperature of the heater portion (belt portion) corresponding to the paper passing portion is raised to 180 ° C. The power supplied to 4 is individually controlled. The power supplied to the individual heating elements 4b-1 and 44b-5 corresponding to the non-sheet passing portion is set to 30 W, which is a small electric power, so that the heater portion (belt portion) corresponding to the non-sheet passing portion and the pressure roller portion Temperature rise is suppressed.

  S403: In the control state of the fixing device 40, A4 portrait size paper passing and fixing processing are started.

  S404: Paper size switching during the movement of the image forming apparatus is monitored. If the paper size continues to be A4 vertical size, the process proceeds to step S405. When the paper size is switched to the A4 landscape size, the process proceeds to step S505. When the paper size is switched to the A5 vertical size, the process proceeds to step S605.

  S405: If the paper size continues to be A4 vertical size, the paper passing and fixing process is continued.

  S408: The predetermined number of sheets to be passed and the fixing process are completed.

  S409: Energization to all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

  S505: The size is switched to A4 horizontal size in step S404.

  S506: With respect to power supply to the heater 44, energization of all the first to fifth individual heating elements 44b-1 to 44b-5 is started (the heater in the entire longitudinal area is ON), and the maximum heating area width A of the heater 44 is set. The full length region is heated to 180 ° C.

In the first embodiment, 400 W of power is applied to the third individual heating element 44b-3 at the longitudinal center. Electric power of 120 W is applied to the first and fifth individual heating elements 44 b-1 and 44 b-5, respectively, and power of 80 W is applied to the second and fourth individual heating elements 44 b-2 and 44 b-4. And each temperature control system including the first to fifth thermistors TH1 to TH5 is adjusted so that the temperature of the heater portion (belt portion) corresponding to each individual heating element is raised to 180 ° C. The power supplied to the individual heating elements is individually controlled.

  S507: In the control state of the fixing device 40, the passing of A4 landscape paper and the fixing process are started.

  S404, S405, S408, S409, S999: The predetermined number of sheets to be passed and the fixing process are completed. Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped. The image forming apparatus 1 is held in a standby state until a start signal for the next image forming job is input.

  S605: The size is switched to A5 vertical size in step S404.

  S606: Regarding the power supply to the heater 44, 400 W is applied to the third individual heating element 44b-3 corresponding to the paper passing portion. A small power of 30 W is applied to each of the first, second, fourth, and 54th individual heating elements 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion.

  The power supply to the individual heating element 44b-3 is controlled by the temperature control system including the thermistor TH3 so that the temperature of the heater portion (belt portion) corresponding to the paper passing portion is raised to 180 ° C. Is done. The power supplied to the individual heating elements 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion is set to a low power of 30 W, so that the heater portion corresponding to the non-sheet passing portion (belt) Part), the temperature rise of the pressure roller part is suppressed.

  S607: In the control state of the fixing device 40, A5 vertical size paper passing and fixing processing are started.

  S404, S405, S408, S409, S999: The predetermined number of sheets to be passed and the fixing process are completed. Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped. The image forming apparatus 1 is held in a standby state until a start signal for the next image forming job is input.

  S101: Referring to FIG. 11C, if the paper size is A5 vertical size in step S101 of FIG. 11A, the process proceeds to step S702.

  S702: When the paper size is A5 vertical size, the fixing device 40 starts to rotate the pressure roller 42 at a predetermined control timing. 400 W for the third individual heating element 44b-3 corresponding to the sheet passing portion, and the first, second, fourth, and 54th individual heating elements 44b-1, 44b-2, 44b corresponding to the non-sheet passing portion. -4 and 44b-5 are each applied with a small power of 30 W.

  The power supply to the individual heating element 44b-3 is controlled by the temperature control system including the thermistor TH3 so that the temperature of the heater portion (belt portion) corresponding to the paper passing portion is raised to 180 ° C. Is done. The power supplied to the individual heating elements 44b-1, 44b-2, 44b-4, and 44b-5 corresponding to the non-sheet passing portion is set to a low power of 30 W, so that the heater portion corresponding to the non-sheet passing portion (belt) Part), the temperature rise of the pressure roller part is suppressed.

  S703: The fixing process of A5 vertical size paper that has been passed in the control state of the fixing device 40 is started.

  S704: Paper size switching during the movement of the image forming apparatus is monitored. If the paper size continues to be A5 vertical size, the process proceeds to step S705. If the paper is switched to A4 landscape size, the process proceeds to step S805. If the paper is switched to A4 vertical size, the process proceeds to step S905.

  S705: When the paper size is still A5 vertical size, the paper passing and fixing process are continued.

  S708: Passing of the predetermined number of sheets and fixing processing are completed.

  S709: Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped.

  S999: The image forming apparatus 1 is held in a standby state until a next image forming job start signal is input.

  S805: The size is switched to A4 horizontal size in step S404.

  S806: Regarding power supply to the heater 44, energization of all the first to fifth individual heating elements 44b-1 to 44b-5 is started (the heater in the entire longitudinal area is ON), and the maximum heating area width A of the heater 44 is set. The full length region is heated to 180 ° C.

In the first embodiment, 400 W of power is applied to the third individual heating element 44b-3 at the longitudinal center. Electric power of 120 W is applied to the first and fifth individual heating elements 44 b-1 and 44 b-5, respectively, and power of 80 W is applied to the second and fourth individual heating elements 44 b-2 and 44 b-4. And each temperature control system including the first to fifth thermistors TH1 to TH5 is adjusted so that the temperature of the heater portion (belt portion) corresponding to each individual heating element is raised to 180 ° C. The power supplied to the individual heating elements is individually controlled.

  S807: In the control state of the fixing device 40, the passing of A4 landscape paper and the fixing process are started.

  S704, S705, S708, S709, S999: The predetermined number of sheets to be passed and the fixing process are completed. Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped. The image forming apparatus 1 is held in a standby state until a start signal for the next image forming job is input.

  S905: The size is switched to A4 vertical size in step S704.

  S906: Regarding the power supply to the heater 44, the third individual heating element 44b-3 has 400 W, the second and fourth individual heating elements 44b-2, 44b-4 have 80 W, respectively, and the first and fifth A power of 30 W is applied to the individual heating elements 4b-1 and 44b-5.

  Then, the individual heating elements 44b-2 to 44b- are provided by the temperature control system including the thermistors TH2 to TH4 so that the temperature of the heater portion (belt portion) corresponding to the paper passing portion is raised to 180 ° C. The power supplied to 4 is individually controlled. The power supplied to the individual heating elements 4b-1 and 44b-5 corresponding to the non-sheet passing portion is reduced from 120W to 30W, so that the heater portion (belt portion) corresponding to the non-sheet passing portion and the pressure roller portion Temperature rise is suppressed.

  S907: In the control state of the fixing device 40, A4 portrait size paper passing and fixing processing are started.

  S704, S705, S708, S709, S999: The predetermined number of sheets to be passed and the fixing process are completed. Energization of all the first to fifth individual heating element layers 44b-1 to 44b-5 is stopped at a predetermined control timing (heater OFF), and the driving of the pressure roller 42 is also stopped. The image forming apparatus 1 is held in a standby state until a start signal for the next image forming job is input.

  In the case where A4 vertical size paper or A5 vertical size paper, which is small size paper, is continuously passed for a long time, the temperature of the pressure roller end (non-sheet passing portion) may rise too much. The power supply may be turned OFF / ON at a predetermined ratio.

  Also, when the maximum size paper is passed, the temperature at the end of the pressure roller is the same as that at the center, so the edge temperature may rise too soon after switching from the maximum size paper to the small size paper. . For this, it is preferable to reduce the power supplied to the individual heating elements corresponding to the non-sheet passing portion of the heater 44 for the first predetermined time when switching from the maximum size paper to the small size paper.

By using the control of the first embodiment, it is possible to set the pressure roller central portion temperature-end portion temperature within a range of ± 20 ° C. Accordingly, it is possible to prevent paper wrinkles and image defects without providing a waiting time until the temperature difference between the paper passing portion and the non-paper passing portion of the pressure roller 42 is alleviated.

(4) Comparison with Comparative Example Next, Example 1 was compared with the comparative example. As operating conditions, the belt rotation speed was 248 mm / s, the applied pressure was 314 N (32 kgf) in total pressure, and the target temperature of the belt 43 was 180 ° C.

  The evaluation method is as described below. First, 150 sheets of A4 size paper (210 mm × 297 mm) of CS-680 (manufactured by Nippon Paper Industries Co., Ltd.) as small size paper is passed in a direction in which the longitudinal direction is 210 mm (A4 vertical size). When the paper feeding is completed, the time until the pressure roller central part temperature (paper feeding part temperature) −edge part temperature (non-paper passing part temperature) falls within the range of ± 20 ° C. is measured. In order not to cause paper wrinkles or image defects when passing thin paper of large size, it is necessary to provide this time as a waiting time.

Fixing device of comparative example 1: In the fixing device 40 of the first embodiment , the heater 44 is a heater in which the full length region of the maximum heating region width A is a single heating element.

  Fixing device of Comparative Example 2: A fixing device in which a cooling fan was provided at the end of the fixing device of Comparative Example 1 was used. When the temperature of the non-sheet passing portion is raised by continuous printing of small size paper, the belt 43 is cooled until the temperature is lowered to a predetermined temperature by a cooling fan.

Fixing device of comparative example 3: using a fixing device having a heater having a plurality of individual heating elements as in the first embodiment , and when passing small size paper, to individual heating elements corresponding to non-sheet passing portions To prevent the power from being turned on.

Table 6 summarizes the required power amount and the required time for changing the paper size in the fixing devices of the first embodiment and the first to third comparative examples.

  In Comparative Example 1, since the non-sheet passing portion is also heated, a required power amount increases and a waiting time occurs until the temperature of the pressure roller end portion (non-sheet passing portion) decreases. The required time has increased significantly.

  In Comparative Example 2, since the edge portion is cooled, the temperature of the end portion (non-sheet passing portion) of the pressure roller 42 does not increase, and the time required for changing the sheet size does not occur. However, since the non-sheet passing portion is also heated and the heated end portion is cooled, the required power is increased.

  In Comparative Example 3, since the non-sheet passing portion is not heated, the amount of power required is small, but a waiting time occurs until the temperature of the central portion of the pressure roller decreases, so the time required for changing the paper size has greatly increased. .

  In this way, even when the paper width is changed from a small size paper to a large size paper, a fixing process that does not cause paper wrinkles or image defects without causing a decrease in productivity due to downtime or the like is performed with a low amount of electric power. It became possible to continue.

Example 2
Next, a description will be given of a second embodiment according to the present invention. The second embodiment pressurizes the first to fifth thermistors TH1 to TH5 for temperature control of the individual heating elements 44b-1 to 44b-5 of the heater 44 in the fixing device 40 in the reference example and the first embodiment. The configuration is arranged with respect to the roller 42.

  That is, as shown in the schematic diagram of FIG. 12, the first to fifth thermistors TH <b> 1 to TH <b> 5 are connected to the heat generation areas A <b> 44 b-1 of the first to fifth individual heating elements 44 b-1 to 44 b-5 of the heater 44. To the surface of the roller portion corresponding to A44b-5. Then, the thermistors TH1 to TH5 measure the temperatures of the roller portions corresponding to the heat generation regions A44b-1 to A44b-5 of the individual heating elements 44b-1 to 44b-5, and the detection results are used for the temperature control of the control unit 24. It is the structure which feeds back to a means part.

The operation of the fixing device 40 is the same as that of the first embodiment , but in the second embodiment , the non-sheet passing portion (the recording material non-passing portion) of the pressure roller 42 is also passed when the small size sheet is passed. Part (recording material passing part) is controlled to be substantially the same temperature. That is, the power supplied to the individual heating element corresponding to the non-sheet passing portion when the small size sheet is passed is determined by the detected temperature of the thermistor corresponding to the sheet passing portion of the pressure roller 42 and the thermistor corresponding to the non-sheet passing portion. It is controlled so that the difference between the detected temperatures becomes substantially zero. Accordingly, the temperature of the pressure roller 42 is controlled so that the entire area of the pressure roller 42, that is, the sheet passing portion is substantially the same temperature as the non-sheet passing portion when small-size paper is passed.

  The temperature of the paper passing portion of the pressure roller 42 varies depending on the paper type (contact thermal resistance, thermal conductivity, heat capacity, etc.) to be passed, the amount of toner forming the image, the number of sheets to be passed, and the like. Further, even if the temperature of the non-sheet passing portion is the same as the electric power to be input, it varies depending on the environmental temperature, the temperature of the pressure roller at the start of sheet passing, and the like.

However, in the second embodiment , the pressure roller 42 is controlled so that the entire region has the same temperature as the central portion even if conditions such as the type of paper to be passed and the environmental temperature change. Therefore, even when the paper width is changed from a small size paper to a large size paper, the fixing process that does not cause paper wrinkles or image defects is continued with a low electric energy without causing a decrease in productivity due to downtime or the like. It became possible.

Example 3
Next, a third embodiment according to the present invention will be described. In the third embodiment , the same fixing device 40 as in the first or second embodiment is used. The control mode of the fixing device 40 described in the first embodiment is set as a first control mode. That is, in the case of passing small-size paper, the temperature of the portion corresponding to the paper passing portion (recording material passage portion) of the pressure roller 42 and the temperature of the portion corresponding to the non- paper passing portion (recording material non-passing portion). The electric power supplied to the individual heating element corresponding to the non-sheet passing portion of the heater 44 is controlled so that the difference between the temperature and the temperature is within the range of ± 20 ° C. This control mode is defined as a first control mode.

Further, in the first embodiment, the control mode of Comparative Example 3 in which the non-sheet passing portion is not heated, that is, in the case of small size paper passing, control is performed so that power is not supplied to the individual heating element corresponding to the non-sheet passing portion. The control mode to be performed is the second control mode.

In the third embodiment, the user can select either the first control mode or the second control mode. First Control Mode The second control mode is selected by the user operating the mode selection unit of the operation unit 27 of the host apparatus 23 or the operation unit 27 (FIG. 1) of the image forming apparatus. A preselection instruction can be made.

Although waiting time occurs in the second control mode, it is possible to reduce the required power amount. Therefore, the user who wants to reduce the amount of power and improve the energy saving performance can select the second control mode in which the non-sheet passing portion is not heated, and the user who places importance on productivity can use the first control mode described in the first embodiment. Enabled selection. Control may be switched between printer and copy.

《Other matters》
1) The heating rotator 43 may be in the form of a roller body. Further, the heating rotator 43 may be in the form of an endless belt that is stretched between a plurality of suspension members and driven to rotate.

  2) An apparatus configuration in which the heating rotator 43 is externally heated by the heating body 44 may be employed.

  3) The pressure rotator 42 may be in the form of an endless belt.

  4) The heating element 44 can be configured to heat each individual heating element by electromagnetic induction, to be heated by a nichrome wire, or to be heated using a halogen heater or an infrared lamp. is there.

  5) It is possible to adopt an apparatus configuration in which paper conveyance is based on one side.

  6) The image heating apparatus according to the present invention reheats the fixed toner image in addition to an apparatus that heats an unfixed toner image (developer image, developer image) and fixes or presupposes it as a fixed image. Thus, an apparatus for modifying the surface properties such as gloss is also included.

  7) The image forming unit of the image forming apparatus is not limited to the electrophotographic system. The image forming unit may be an electrostatic recording system or a magnetic recording system. Further, the toner image is not limited to the transfer method, and a toner image may be formed directly on the recording material.

  8) In the embodiment, the fixing device 40 may be implemented by an image forming apparatus other than the electrophotographic printer of the embodiment, a color copying machine, a facsimile, a color printer, a composite machine thereof, or the like. That is, the fixing device and the electrophotographic printer of the example are not limited to the combination of the above-described constituent members, and may be realized in another embodiment in which a part or all of the replacement members are replaced.

  9) In this embodiment, when fixing a small size paper after fixing a large size paper, the operation of the fixing device as shown in the present embodiment may not be performed.

  10) In this embodiment, the operation of the heating source may be turned on and off intermittently.

  11) In this embodiment, when the user operates the fixing device so as not to perform this operation, the operation shown in this embodiment may not be performed.

  40 .. Image heating device, 43 .. Heating rotator, 42 .. Pressurizing rotator, 44 .. Heating body, 44 b-1 to 44 b-5, Multiple heating elements, 24.・ Recording material

Claims (10)

A heating rotor,
A pressure rotator that forms a nip portion for sandwiching and conveying the recording material carrying an image with the heating rotator and heating the recording material; and
A heating body for heating the heating rotator, the heating body having a plurality of heating elements that are arranged side by side along the longitudinal direction of the heating rotator and individually generate power and generate heat;
When energizing all of the plurality of heating elements at the time of starting up the apparatus, when continuously introducing a recording material having a width smaller than the maximum width size recording material that can be introduced into the apparatus and heating, While controlling the amount of electric power supplied to the heating element corresponding to the recording material passing portion so that the temperature of the portion corresponding to the recording material passing portion of the heating rotator is maintained at a predetermined image fixing temperature. The difference between the temperature of the portion corresponding to the recording material non-passing portion of the pressing rotator and the temperature of the portion corresponding to the recording material passing portion of the pressing rotator is maintained within a range of ± 20 ° C. The amount of power input to the heating element corresponding to the recording material non-passing portion is controlled, and when the introduction of the predetermined number of recording materials and the heating process are completed, all of the plurality of heating elements are applied. A control unit that stops energization and holds the device in a standby state ;
An image heating apparatus comprising:   The control unit, based on a pre-selected instruction, the temperature of the portion corresponding to the recording material non-passing portion of the pressure rotator and the portion corresponding to the recording material passage portion of the pressure rotator. A first control mode for controlling the amount of power input to the heating element corresponding to the recording material non-passing portion so that the difference from the temperature is maintained in a range of ± 20 ° C., and the heating element The image heating apparatus according to claim 1, wherein the second control mode in which power is not input is selectively executed.   The recording is performed such that the temperature of the portion corresponding to the recording material non-passing portion of the pressure rotating body is maintained at the temperature corresponding to the temperature of the portion corresponding to the recording material passing portion of the pressing rotating body. 3. The image heating apparatus according to claim 1, wherein the amount of electric power supplied to a heating element corresponding to the material non-passing portion is controlled.   The image heating apparatus according to any one of claims 1 to 3, wherein the pressure rotator has a larger expansion amount during heating than the heating rotator.   The total heat generation width of the heat generation areas of the plurality of heat generating elements is the maximum heat generation area width of the heating element, and substantially corresponds to the width size of the recording material having the maximum width size. Item 5. The image heating apparatus according to any one of Items 1 to 4.   The heating rotator is an endless belt having flexibility, the heating rotator is provided inside the belt, and the heating body and the pressure rotator are pressed against each other with the belt interposed therebetween. The image heating apparatus according to claim 1, wherein a portion is formed.   The image heating apparatus according to claim 6, wherein the pressure rotator is driven to rotate, so that the belt rotates following sliding with respect to the heating body.   The image heating apparatus according to claim 6, wherein the heating body is fixed and held on a holding member.   The image heating apparatus according to claim 1, wherein the pressure rotator is an elastic roller.   An image forming apparatus comprising the image heating apparatus according to claim 1.